Latching relay assembly

ABSTRACT

A latching relay assembly is disclosed herein and generally comprises first and second elongated latching members which are mounted to opposite legs of an L-shaped bracket for pivotal movement between biased unlatched positions and latched positions. A cam roller mounted on and carried by the first latching member and a notch formed with the second latching member cooperate with each other for locking only one of the members in its respective latched position at any given time. First and second electromagnetic solenoids are positioned adjacent the first and second members respectively, and, upon energization, drive their associated members from the unlatched to latched position, wherein the solenoids are immediately deenergized.

United States Patent Komar [54] LATCHING RELAY ASSEMBLY [72] Inventor: Mitchell F. Komar, 2334 North Monitor Ave., Chicago, Ill. 60639 [22] Filed: Oct. 2, 1970 21 Appl. No.: 77,580

[52] US. Cl. ..335/169, 200/169 [51] Int. Cl. ..l-l0lh 3/20 [58] Field of Search ..335/20, 160, 167, 168, 169,

[56] References Cited UNITED STATES PATENTS 2,819,364 1/1958 Jaidinger ..335/16l 1,971,199 8/1934 Owens ..335/169 3,240,899 3/1966 Lawrence et al. ..335/l60 2,916,583 12/1959 Noyes ..335/l70 [451 Sept. 26, 1972 Primary Examiner-Harold Broome Attorney-Olson, Trexler, Wolters & Bushnell [5 7] ABSTRACT A latching relay assembly is disclosed herein and generally comprises first and second elongated latching members which are mounted to opposite legs of an L-shaped bracket for pivotal movement between biased unlatched positions and latched positions. A cam roller mounted on and carried by the first latching member and a notch formed with the second latching member cooperate with each other for locking only one of the members in its respective latched position at any given time. First and second electromagnetic solenoids are positioned adjacent the first and second members respectively, and, upon energization, drive their associated members from the unlatched to latched position, wherein the solenoids are immediately deenergized.

9 Claims, 7 Drawing Figures LATCHING RELAY ASSEMBLY SUMMARY OF THE INVENTION This invention relates generally to electrical relays and more particularly to electromagnetically actuated latching relays.

BACKGROUND OF THE INVENTION Prior art latching relays are known to include latching members mounted to a support structure for alternate movement between latched and unlatched positions. Most of these types of relays employ some kind of dog or pawl to accomplish the latching operation. It has been found that these prior art relays have difficulty in releasing the dog or pawl, as a result of wear or misalignment of the parts. Moreover, vibrations imparted to the device can sometimes unlatch the relay accidentally.

Accordingly, an important general object of the present invention is to provide a new and improved electromagnetically actuated latching relay assembly which is more reliable in operation than those of the prior art.

Another object of the present invention is to provide a new and improved electromagnetically actuated latching relay which minimizes wear or misalignment of the various parts for maximizing reliability thereof.

Still another object of the present invention is to provide a new and improved electromagnetically actuated latching relay which is substantially unaffected in its operation by vibrations imparted thereto.

A further object of the present invention is to provide a latching assembly of the above described kind which requires minimal electrical power for the operation thereof.

I A more particular object of the present invention is to provide a latching relay of the above described kind which is initially electromagnetically actuated, but which is mechanically maintained in its actuated state.

The aforementioned objects are attained and the prior art deficiencies are eliminated by the provision of a latching'relay assembly constructed in accordance with the present invention. Briefly, the assembly includes first and second elongated latching arms, each of which is mounted on a respective leg of an L-shaped support bracket for pivotal movement between a latched and unlatched position. The latching arms are spring biased in their unlatched positions and are alternately electromagnetically driven to their latched positions by associated solenoids.

Upon energization of the solenoid associated with the first latching arm, the latter is driven to its latched position whereupon a rotatable element or cam roller carried thereby engages a notch on the second latching arm and thereby prevents the first arm from moving back to its biased unlatched position. The first solenoid is immediately deenergized, which restricts the latching operation solely to a mechanical one.

Energization of the other solenoid drives the second latching arm from its biased unlatched position to its latched position, which removes the cam roller from the notch, allowing the first latching arm to move back to its biased unlatched position. In this condition, the cam roller engages a surface on the second latching arm that is adjacent to the notch for preventing the second latching member for moving back to its unlatched position. The second solenoid may then be immediately deenergized.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 is a partially broken elevational view of a latching relay assembly constructed in accordance with the present invention, the assembly being shown in a first state;

FIG. 2 is a sectional view taken generally along line 22 in FIG. 1;

FIG. 3 is a partially broken elevational view of the latching relay assembly of FIG. 1, the assembly being DETAILED DESCRIPTION Turning now to the drawings, wherein like components are designated by like reference numerals throughout the various figures, a latching relay assembly constructed in accordance with the present invention is illustrated in FIG. 1 and generally designated by the reference numeral 10. The assembly includes an L-shaped base or support 1 l defined by equally extending legs 12 and 14, each of which respectively carries a latch arm arrangement 16 and 18 for pivotal movement between a biased unlatched position and a latched position to thereby actuate an associated assembly of contacts 20 and 22. The latch arm arrangements and contact assemblies are mounted to their associated legs by respective extension or connecting blocks 24 and 26 which in turn are fixed to legs 12 and 14 in a known manner.

In accordance with the present invention, a latch assembly 27 is provided for alternatively mechanically maintaining the latch arm arrangements in their latched positions and comprises a cylindrical cam roller element 29 carried by arm arrangement 16, in a manner to be described hereinafter. The end of the arm arrangement 18 has a notch 106 having a shoulder 31. Likewise the arm arrangement 18 has an end shoulder 33 that is perpendicular to the shoulder 31.

With the arm arrangement 16 in its biased unlatched position and the arm arrangement 18 in its latched position, as illustrated in FIGS. 1 and 5, the cam roller 29 rests against the shoulder 31 for preventing the arm arrangement 18 from moving to its latched position.

Upon electromagnetically driving the arm arrangement 16 to its latched position, in a manner to be described hereinafter, the cam roller 29 is removed from the shoulder 31, for allowing the arm arrangement 18 to move to its biased unlatched position, as illustrated in FIGS. 3 and 6. In this position, the cam roller lodges against the shoulder 33 and thereby prevents arm arrangement 16 from moving to its biased unlatched position. Since the latch assembly 27 does not utilize moving parts such as the typical dog or pawl, misalignment and wear is substantially eliminated. In addition, as will be seen hereinafter, this type of latching arrangement requires minimal electrical current for operation thereof.

Attention is directed to the latch arm arrangement 16 which is shown to include an L-shaped fulcrum or flange 28 having one leg thereof in confronting relationship with and suitably fastened to connecting block 24 at a point near the vertex of the L-shaped support while the other leg 29 of the flange extends upwardly for rockably supporting an elongated substantially rectangular latching or actuating arrn 30 at a point slightly to the left of the actuating arms center, as illustrated in FIG. 1.

A substantially square support plate 32, illustrated best in FIG. 2, is mounted to the downwardly facing surface of the latching or actuating arm 30 by bolt and nut assemblies 34 and includes a T-shaped extension 36 extending rearwardly of the plate. The T-shaped extension 36 and interconnecting plate 32 cooperate to receive laterally spaced legs 38. The legs 38 are formed on a member 40 that is secured to the leg 29. In this manner, latching or actuating arm 30 is free to pivot about the fulcrum, while simultaneously being restricted in its lateral and longitudinal movement relative thereto.

Turning to FIG. 2, a pair of elongated rectangular extension arms 42 are mounted to the top surface of support plate 32 on opposite sides of latching or actuating arm 30 by screw and nut assemblies 44 and extend a substantial distance beyond the left end of the actuat ing arm, as viewed in FIG. 2. The extension arms 42 have enlarged ends 42a which are provided by arm sections 43 that are welded or otherwise secured in place. As best seen in FIG. 4, the enlarged ends 42a are cut away for receiving aligned bearings 45 for joumalling the cam roller 29. Snap rings 45a or like retainers on the roller 29 may be used to prevent axial separation from the bearings 45.

- Returning to FIG. 1, latching or actuating arm 30 is pivotally biased in an unlatched position, by a pair of elongated spring elements 48 and 50, the first of which is suitably rigidly held at opposite ends to actuating arm 30 and extension block 24 at a point adjacent L-shaped flange 28. The second mentioned spring element 50 is suitably fastened at opposite ends to the actuating arm 30 and the top elongated block of a plurality of additional extension blocks 52, 52 which in turn are mounted in stacked relationship to the extension or connecting block 24. As illustrated in FIG. 1, the spring element 50 is positioned near the right end of the actuating arm 30, a substantial distance from spring element 48. In this manner, the right end of actuating arm 30 tends to move towards leg 12 of L-shaped base or support 11, while the left end of the arm tends to move away from leg 12, the movement being limited by a stopper element 54 (FIG. I) mounted on the top extension block 52 and positioned adjacent spring element 50. A longitudinal guide screw 56 capped at the top end 58 extends through an aperture 60 in the right end of the actuating arm 30 and is mounted through and to extension blocks 52 and 24 by a plurality of nuts 61 for aiding in the guidance of the actuating arm 30 during pivotal movement thereof.

' The arm 30 is driven from its biased unlatched position, as viewed in FIG. 1, to its latched position, as

viewed in FIG. 3, by an electromagnetic solenoid or coil 62 which is suitably mounted to one leg of L-' shaped flange 28, and which is positioned such that its electromagnetic attracting element 64 rests slightly below the support plate 32 when the latching or actuating arm is in its biased unlatched position. In this manner, upon energization of the solenoid, the support plate 32, which is constructed of magnetic material, is magnetically attracted to element 64 of the solenoid, causing the extension arms 42, cam roller 29 and the left end of latching arm 30 to move downwardly about L-shaped flange 28.

Attention is now directed to the contact assembly 20 which comprises a pair of laterally spaced mounting blocks (FIG. 2), each of which is in the form of a plurality of individual electrical insulating pads 72 held in stacked relationship by a pair of end plates 74. The mounting blocks are positioned on oppositesides of latching arm 30 and extend upwardly from extension block 24 at points adjacent spring element 48, the mounting blocks being rigidly held to the extension block by a plurality of elongated screws and cooperating nuts 76.

Each of the mounting blocks includes a pair of fixed contact blades 78 and 80, preferably in the form of reed switch contacts which are mounted on opposite sides of a common insulating pad 72 and which extend a substantial distance to the right of the mounting block, as viewed in FIG. 1, where they electrically and mechanically engage associated movable contacts to be described below. In addition, the fixed contacts extend outwardly to the left of mounting block 70 where they may be appropriately electrically connected to external lead wires (not shown). In order to reduce the resiliency of contacts 78 and 80 and thereby maintain them substantially rigid, the three insulating pads 72, which directly confine the contacts, extend a substantial distance beyond the remaining insulating pads.

A resiliently movable upper contact blade 84 and a resiliently movable lower contact blade 88, both of which also are preferably in the form of reed switch contacts, are respectively supported above and below the fixed contact blades 78 and 80 by mounting blocks 70, and are electrically insulated from the fixed contacts by intermediate pads 72. As illustrated in FIG. 1, the movable contact blades extend outwardly from both sides of mounting blocks 70, so that their left ends may connect with external lead wires (not shown), while their right ends make electrical contact with an associated fixed contact blade. The contact blades 84 and 88 are biased in electrical and mechanical engagement with their associated fixed contacts 78 and 80 by respective adjacent deformed reed type contact blades 82 and 86, which tend to straighten out and, in so doing, force their associated movable contacts towards the fixed contacts.

As illustrated in FIG. 2, an insulated elongated contact actuating member is supported by and extends from opposite sides of latching arm 30 and is positioned between each set of contact blades 84 and 88. With the latching arm in its biased unlatched position, as illustrated in FIG. 1, member 90 forces the contact blades 88 away from and out of engagement with their associated fixed contact blades 80. In like manner, when the actuating arm is moved to its latched position, as illustrated in FIG. 3, member 90 drives the contact blades 84 out of engagement with their associated fixed contacts 78, whereby contact blades 88 are allowed to move into engagement with their associated fixed contacts. In this manner,.external electrical components (not shown) may be energized and deenergized, depending upon the position of actuating arm 30.

Attention is directed to the latch arm arrangement 18 which is shown to include an L-shaped fulcrum or flange 92 having one leg thereof in confronting relationship with and suitably fastened to connecting block 26 at a point near the vertex of the'L-shaped support while the other leg of the flange extends outwardly for rockably supporting an elongated substantially rectangular latching or actuating arm 94 at a point slightly below the actuating arms center, as illustrated in FIG. 3.

A substantially square support plate 96, illustrated best in FIG. 4, is mounted to the inwardly facing surface of the latching or actuating arm by bolts and nuts 98, and includes a- T-shaped extension 100 extending above the plate 96. The T-shaped extension and interconnecting plate 96 cooperate to receive laterally spaced legs 102 extending from and formed with a flange 104 that is suitably mounted on the L-shaped fulcrumflange 92. In this manner, latching or actuating arm 94 is free to pivot about the fulcrum, while simultaneously being restricted in its lateral and longitudinal movement relative thereto.

Latching or actuating arm 94 is pivotally biased in an unlatched position by a pair of elongated spring elements 112 and 114, the first of which is suitably rigidly held at opposite ends to actuating arm 94 and-extension block 26 at a point adjacent L-shaped flange 92. The second mentioned spring element 114 is suitably fastened at opposite ends to the actuating arm 94 and the top elongated block of a plurality of additional extension blocks 118, which in turn are mounted in stacked relationship to the extension or connecting block 26. As illustrated in FIG. 3, the spring element 114 is positioned near the top of the actuating arm 94,

a substantial distance from spring element 112. In this manner, the top of actuating arm 94 tends to move towards leg 14 of L-shaped base or support 11, while the lower end of the arm tends to move away from leg 14, the movement being limited by a stopper element 120 mounted to the top extension block 118 and positioned adjacent spring element 114. A longitudinal guide screw 122 capped at the end 124 extends through an aperture 126 in the end of the actuating arm 30 and is mounted through and to extension blocks 118 and 26 by a plurality of nuts 128 for aiding in the guidance of the actuating arm during pivotal movement thereof.

The latching or actuating arm 94 is driven from its biased unlatched position, as viewed in FIG. 3, to its latched position, as viewed in FIG. 1, by an electromag- 'neticrsolenoid or coil 130 which is suitably mounted to one leg of L-shaped flange 92, and which is positioned such that its electromagnetic attracting element 132 rests adjacent to the support plate 96 when the latching or actuating arm is in its biased unlatched position. In this manner, upon energization of the solenoid, the support plate 96, which is constructed of magnetic material, is magnetically attracted to element 132 of the solenoid, causing the latching arm 94 to move about L- shaped fulcrum flange 92.

Attention is now directed to the contact assembly 22 which comprises a pair of laterally spaced mounting blocks 134 (FIG. 4) each of which is in the form of individual electrical insulating pads 136 held in stacked relationship by a pair of end plates 138. The mounting blocks are positioned on opposite sides of latching am 94 and extend upwardly from extension block 26 at points adjacent spring element 112, the mounting blocks being rigidly held to the extension block by a plurality of elongated screws and cooperating nuts 140.

Each of the mounting blocks includes a pair of fixed contact blades 142 and 144, preferably in the form of reed switch contacts, which are mounted on opposite sides of a common insulating pad 136 and which extend a substantial distance to the left of the mounting block, as viewed in FIG. 3, where they electrically and mechanically engage associated movable contacts, to be described below. In addition, the fixed contacts extend outwardly from the mounting block 138 where they may be appropriately electrically connected to external lead wires (not shown). In order to reduce the resiliency of contacts 142 and 144 and thereby maintain them substantially rigid, the three insulating pads 136 which directly confine the contacts extend a substantial distance beyond the remaining insulating pads.

A resiliently movable upper contact blade 146 and a resiliently movable lower contact blade 148, both of which are also preferably in the form of reed switch contacts, are respectively supported on opposite sides of the fixed contact blades 142 and 144 by an associated mounting block 134 and are electrically insulated from the fixed contacts by intermediate pads 136. As illustrated in FIG. 3, the movable contact blades extend outwardly from above and below the mounting blocks 138, so that their lower ends may connect with extended lead wires (not shown), while their upper ends can make electrical contact with an associated fixed contact blade. The contact blades 146 and 148 are biased in electrical and mechanical engagement with their associated fixed contacts 142 and 144 by respective adjacent deformed reed type contact blades 150 and 152, which tend to straighten out and, in so doing, force their associated movable contacts towards the fixed contacts.

As illustrated in FIG. 4, an insulated elongated contact actuating member 154 is supported by and extends from opposite sides of latching arm 94, and is positioned between each set of contact blades 146 and 148. With the latching arm in its biased unlatched position,

as illustrated in FIG. 3, member 154 forces the contact blades 148 away from and out of engagement with their associated fixed contact blades 144. In like manner, when the actuating arm is moved to its latched position, as illustrated in FIG. 1, member 154 drives the contact blades 146 out of engagement with their associated fixed contacts 142, whereby contact blades 148 are al-.

' lowed to move into engagement with their associated fixed contacts. In this manner, external electrical components (not shown) may be energized and deenergized, depending upon the position of actuating arm With latching relay assembly 10 constructed in the aforementioned manner, attention is directed to the manner in which actuating arms 30 and 94 are alternatively held in their latched positions. As illustrated in FIGS. 1 and 5, when the actuating arm 30 is in its manner the actuating arm 94 is held in its latched position, even though associated electromagnetic solenoid 130 is in a deenergized state. Upon energizing solenoid 62, the actuating arm 30 is driven to its latched position, as illustrated in FIG. 3, so that the cam roller 29 is dislodged from within notch 106. This allows the actuating arm 94 to move to its biased unlatched position and places the shoulder 33 thereof against the top of cam roller 29, and thereby prevents the actuating arm 30'from moving to its biased unlatched position. In this regard, it should be noted that the holding or latching operation is entirely a mechanical one which does not require the utilization of electromagnetic solenoids 62 and 130, except insofar as to initially drive the actuating arms to their latched position. Accordingly, these solenoids may be immediately deenergized upon receipt of their associated actuating arms. Furthermore, the cam roller 29, being rotatable, does not tend to wear in one spot as in the case of pawl mechanisms.

In order to deenergize the solenoids 62 and 130 immediately after energization thereof, attention is directed to FIG. 7, which shows the solenoids connected in electrical series with respective operating switches 160 and 162 which are spring biased opened and respective contact blade sets 148, 144 and 80, 88. While the solenoids are preferably energized by a common direct current source 164, it is tobe understood that individual power sources or alternating current power sources may be provided.

Assuming that actuating arm 30 is in its unlatched biased position while actuating arm 94 is in its latched position, the contact blades 144 and 148, as illustrated in FIG. 7, are closed while the contact blades 80 and 88 are opened. Upon actuation of switch 160, the circuit between the solenoid 62 and power supply 164 is closed for energizing the solenoid 62 which, as stated above, drives its associated actuating arm 30 to the latched position, and simultaneously allows the actuating arm 94 to move to its biased unlatched position. Upon reaching these positions, the contact blades 144 and 148 are disengaged for opening the circuit between the solenoid 62 and power supply, for thereby deener-- gizing the solenoid while the contact blades 80 and 88 are closed. In this manner, actuation of push-button 162 will reverse the procedure. It is apparent that by relying on the contact blades for deenergizing the solenoids, a minimal amount of current is used independent of the amount of time that the operating switches are I held closed, which, in turn, eliminates the guess work on the part of the operator as to the amount of time required for maintaining the switches in their closed positions.

Returning briefly to FIG. 3, it should be noted that each of the legs 12 and 14 of the L-shaped support 11 may include a respective wire terminal box 164, 166 for centralizing the external wires (not shown) entering and leaving the relay assembly.

While a particular embodiment of the invention has been shown, it should be understood, of course, that the invention is not limited thereto since many modifications may be made. It is, therefore, contemplated to cover by the present application any such modifications as fall within the true spirit and scope of the appended claims.

The invention is claimed as follows: 7

1. A relay assembly comprising: support means; a first latching member mounted on said support means for movement between a latched position and an unlatched position, said first latching member including a cam surface movable therewith; a second latching member mounted to said support means for movement between a latched position and an unlatched position; said second latching member including a first surface cooperating with said cam surface for maintaining said first latching member in its latched position when said second latching member is an unlatched position and a second surface cooperating with said cam surface for maintaining said second member in a latched position when said first member is in an unlatched position, said first and second surfaces having the planes thereof transverse to one another.

2. An assembly according to claim 1 wherein said latching member are biased toward their respective unlatched positions whereby, upon movement of one of said members from its unlatched position to a latched position, the other of said members automatically moves to its unlatched position.

3. An assembly according to claim 2 wherein said cam surface includes a cam roller engaging said first surface when said first member is in its latched position and said second member is in its unlatched position for preventing said first member from moving to its unlatched position, and wherein said second surface engages said cam roller when said second member is in its latched position and said first member is in its unlatched position for preventing said second member from moving to its unlatched position.

4. An assembly according to claim 3 including electrical actuating means for alternatively moving said latching members from their latched positions to their unlatched positions, power supply means for energizing said electrical actuating means whereby to move said members from their unlatched positions to their latched positions, and disconnecting means for deenergizing said electrical actuating means when said latching members reach their latched positions.

5. An assembly according to claim 4 wherein said electrical actuating means includes first and second electromagnetic solenoids for magnetically attracting said latching members from their unlatched to latched positions upon energization of said solenoids, said disconnecting means includes first and second contact means respectively connected in series with said first and second solenoids and said power supply means and respectively responsive to the movement of said second and first latching members from their latched to unlatched positions for opening the circuit between said power supply and said first and second solenoids respectively, whereby to deenergize said first and second solenoids.

6. In an electromagnetic relay structure having first and second movable latching members, means movably supporting each latching member for movement between its latched position and its unlatched position, at least one of said members being in operative connection with at least one electrical contact for opening or closing at least one circuit upon movement of the latching member from one of its said positions to the other position, electromagnetic means actuatable for moving each member to its latched position, means for returning each latching member to its unlatched position, and holding means for holding each latching member in its latched position upon movement thereto and deactuation of the electromagnetic means moving the same; said holding means comprising an element on one of said members and surface portions on the other of said elements, said surface portions having their planes transverse to one another, said element engaging one of said surface portions when the first member is in its latched position and the second member is in its unlatched position and said element engaging another of said surface portions when the second member is in its latched position and the first member is in its unlatched position, and the returning means of the latched member biasing the latched member against the unlatched member at the engagement of said element and surface engaged thereby.

7. Structure according to claim 6 wherein said surface portions are adjacent and are at an angle to each other, and said element is mounted on said one. 

1. A relay assembly comprising: support means; a first latching member mounted on said support means for movement between a latched position and an unlatched position, said first latching member including a cam surface movable therewith; a second latching member mounted to said support means for movement between a latched position and an unlatched position; said second latching member including a first surface cooperating with said cam surface for maintaining said first latching member in its latched position when said second latching member is an unlatched position and a second surface cooperating with said cam surface for maintaining said second member in a latched position when said first member is in an unlatched position, said first and second surfaces having the planes thereof transverse to one another.
 2. An assembly according to claim 1 wherein said latching member are biased toward their respective unlatched positions whereby, upon movement of one of said members from its unlatched position to a latched position, the other of said members automatically moves to its unlatched position.
 3. An assembly according to claim 2 wherein said cam surface includes a cam roller engaging said first surface when said first member is in its latched position and said second member is in its unlatched position for preventing said first member from moving to its unlatched position, and wherein said second surface engages said cam roller when said second member is in its latched position and said first member is in its unlatched position for preventing said second member from moving to its unlatched position.
 4. An assembly according to claim 3 including electrical actuating means for alternatively moving said latching members from their latched positions to their unlatched positions, power supply means for energizing said electrical actuating means whereby to move said members from their unlatched positions to their latched positions, and disconnecting means for deenergizing said electrical actuating means when said latching members reach their latched positions.
 5. An assembly according to claim 4 wherein said electrical actuating means includes first and second electromagnetic solenoids for magnetically attracting said latching members from their unlatched to latched positions upon energization of said solenoids, said disconnecting means includes first and second contact means respectively connected in series with said first and second solenoids and said power supply means and respectively responsive to the movement of said second and first latching members from their latched to unlatched positions for opening the circuit between said power supply and said first and second solenoids respectively, whereby to deenergize said first and second solenoids.
 6. In an electromagnetic relay structure having first and second movable latching members, means movably supporting each latching member for movement between its latched position and its unlatched position, at least one of said members being in operative connection with at least one electrical contact for opening or closing at least one circuit upon movement of the latching member from one of its said positions to the other position, electromagnetic means actuatable for moving each member to its latched position, means for returning each latching member to its unlatched position, and holding means for holding Each latching member in its latched position upon movement thereto and deactuation of the electromagnetic means moving the same; said holding means comprising an element on one of said members and surface portions on the other of said elements, said surface portions having their planes transverse to one another, said element engaging one of said surface portions when the first member is in its latched position and the second member is in its unlatched position and said element engaging another of said surface portions when the second member is in its latched position and the first member is in its unlatched position, and the returning means of the latched member biasing the latched member against the unlatched member at the engagement of said element and surface engaged thereby.
 7. Structure according to claim 6 wherein said surface portions are adjacent and are at an angle to each other, and said element is mounted on said one member to permit rotation of the element thereon upon movement of said members to and from their latched and unlatched positions.
 8. An assembly according to claim 1 wherein said first and second cam surfaces are perpendicular to one another.
 9. An assembly according to claim 6 wherein said surface portions are perpendicular to one another. 